Plastic tubings are extensively employed in the medical field, particularly for patient analysis and treatment procedures. Various FDA-approved plastics and combinations thereof are used, depending upon the specific properties the intended application demands. The selection of desired plastic materials is further limited by the use of the tubing in the in vivo treatment of human patients, as the tubing may be used in the administration of intravenous fluids or itself may be introduced into the body. Thus, numerous factors must be considered in ascertaining which materials to choose.
Polyvinyl chloride (PVC) is a material previously used to make tubing, made with suitable plasticizers necessary to enhance flexibility and other properties. However, such plasticizers or similar additives have a tendency to migrate, causing hazardous contamination with the fluid being transferred through the tubing. The contamination becomes more serious where the fluid is introduced into the body, as contamination of the blood may result. Moreover, plasticized PVC tubings have been shown to absorb nitroglycerin and insulin, and are thus unsatisfactory for the administration of these medicines. Much effort has been directed towards finding an alternative that does not suffer from the limitations of the plasticized PVC tubing.
Polyurethane has been used as an alternative to PVC in medical tubing, as in U.S. Pat. No. 4,211,741 to Ostoich. Polyurethane may be used without plasticizers and other additives, because it is a relatively soft, flexible plastic. Therefore, the possibility of the migration of additives and subsequent contamination are eliminated. In addition, polyurethane exhibits good fluid-flow characteristics. However, the high cost of polyurethane has limited its use to only extraordinary applications.
Some grades of ethylene-vinyl acetate copolymer (EVA) are currently being used as an outer layer, together with low-density polyethylene (LDPE) as an inner layer in forming composite tubing. Although this composite exhibits excellent peel strength, it lacks flexibility, clarity, and is easily scuffed or roughened. In addition, it cannot be solvent bonded. Since the tubing is the connecting link between a reservoir of fluid (nitroglycerin, insulin, etc.) and the patient, the method of connecting the tubing is an important consideration. Where, as here, solvent bonding cannot be utilized, an expensive, less reliable mechanical means of assembly is required, whereby a PVC layer must be pressure fit over the EVA-LDPE tubing to utilize the solvent-bondable characteristics of PVC. For these reasons, the EVA-LDPE product has proven to be unsatisfactory.
U.S. Pat. No. 4,627,844 to Schmitt (“Schmitt”) provides a well-received alternative that includes a tri-layer tube. A commercially successful embodiment of U.S. Pat. No. 4,627,844 is sold under the trademark “SUREPATH 151” by the Plastron/Natvar Division of Tekni-Plex, Inc. As disclosed in Schmitt, an outer layer of PVC and an inner fluid-contact layer of LDPE are co-extruded with an intermediate tie layer of EVA. However, while Schmitt greatly reduces the possibility for the migration of additives from the PVC to the fluid by providing an LDPE fluid-contact layer, the elimination of the PVC is preferred.
In addition to the potential migration problem of PVC additives into a fluid being transferred within a PVC tube, PVC production, use, and disposal are the subject of many regulatory concerns, particularly in Europe. For example, steps must be taken to reduce introduction of vinyl chloride and additives into wastewater during production, and PVC must frequently be incinerated prior to introduction to a landfill. These steps are recommended to prevent introduction of PVC and other additives to the environment due to possible carcinogenic properties demonstrated by these compositions.
Therefore, there is a need for a co-extruded tubing that excludes PVC while providing the advantages of being solvent-bondable, EtO- and gamma-stable, and water-clear that may be used in the administration of nitroglycerin and insulin.